Pharmacogenomics Practice Questions

Q: Which antitubercular drug metabolism is under genetic control?

Isoniazid. **Explanation:** The correct answer is **Isoniazid (INH)**. Its metabolism is a classic example of pharmacogenetics, specifically involving the **N-acetyltransferase 2 (NAT2)** enzyme in the liver. **1. Why Isoniazid is Correct:** Isoniazid is metabolized via **acetylation**. Due to genetic polymorphism in the *NAT2* gene, individuals are categorized into two phenotypes: * **Fast Acetylators:** They metabolize the drug quickly, leading to lower plasma levels and a higher risk of **treatment failure** or sub-therapeutic responses. * **Slow Acetylators:** They metabolize the drug slowly, leading to higher plasma levels and an increased risk of **peripheral neuropathy** (due to Vitamin B6 deficiency) and drug-induced lupus. **2. Why other options are incorrect:** * **Rifampicin:** It is primarily metabolized by deacetylation and is a potent inducer of CYP450 enzymes, but its metabolism is not significantly dictated by a specific genetic polymorphism like INH. * **Cyclosporine:** This is an immunosuppressant (not an antitubercular drug) metabolized by CYP3A4. While CYP3A4 has variations, it is not the classic example of genetic control in the context of TB therapy. * **Pyrazinamide:** It is converted to pyrazinoic acid by the enzyme pyrazinamidase. While resistance can occur due to bacterial gene mutations (*pncA*), its human metabolism is not a major focus of clinical pharmacogenetics. **High-Yield Clinical Pearls for NEET-PG:** * **Acetylation** also affects the metabolism of **Hydralazine, Procainamide, and Sulfonamides** (Mnemonic: **SHIP** - Sulfonamides, Hydralazine, Isoniazid, Procainamide). * **Slow acetylators** are more prone to **Drug-Induced Lupus Erythematosus (DILE)**. * To prevent peripheral neuropathy in slow acetylators taking INH, always co-administer **Pyridoxine (Vitamin B6)** at 10–50 mg/day.

Q: Pharmacogenetics is associated with:

All of these. **Explanation:** **Pharmacogenetics** is the study of how genetic variations (polymorphisms) influence an individual’s response to drugs [1]. It encompasses both **pharmacokinetics** (what the body does to the drug) and **pharmacodynamics** (what the drug does to the body). 1. **Variability of enzyme action (Option A):** This is the most classic example of pharmacogenetics [2]. Genetic polymorphisms in Phase I (e.g., CYP2D6, CYP2C19) and Phase II (e.g., NAT2, TPMT) enzymes lead to "fast" or "slow" metabolizer phenotypes, significantly altering drug levels [1]. 2. **Individual variability in oral absorption (Option B):** Genetic variations in drug transporters, such as **P-glycoprotein (MDR1)** or Organic Anion Transporting Polypeptides (OATPs) in the gut epithelium, dictate how much of a drug enters the systemic circulation [1]. 3. **Different dose-response relationships (Option C):** This refers to pharmacodynamic variability. Mutations in drug targets (receptors, ion channels, or enzymes) can change a drug’s affinity or efficacy. For example, polymorphisms in the **VKORC1** gene alter the sensitivity to Warfarin, requiring different doses to achieve the same anticoagulant effect. Since genetic factors influence absorption, metabolism, and receptor sensitivity, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Slow Acetylators (NAT2 deficiency):** Prone to peripheral neuropathy with **Isoniazid** and drug-induced Lupus with **Hydralazine/Procainamide** [1]. * **Pseudocholinesterase deficiency:** Leads to prolonged apnea after **Succinylcholine** administration. * **TPMT deficiency:** Increases the risk of life-threatening bone marrow suppression with **6-Mercaptopurine** and **Azathioprine**. * **HLA-B*1502:** Strongly associated with Stevens-Johnson Syndrome (SJS) in patients taking **Carbamazepine**.

Q: A partial agonist has:

High affinity but low intrinsic activity. ### Explanation To understand this concept, we must distinguish between **Affinity** (the ability of a drug to bind to a receptor) and **Intrinsic Activity/Efficacy** (the ability of a drug to activate the receptor and produce a biological response). **1. Why Option A is Correct:** A **Partial Agonist** is a drug that binds to a receptor (High Affinity) but produces a sub-maximal response even when all receptors are occupied (Low Intrinsic Activity). On a scale of 0 to 1, the intrinsic activity of a partial agonist is between **0 and 1**. Because it competes for the same site as a full agonist but produces a weaker response, it can act as a **functional antagonist** in the presence of a full agonist. **2. Why Other Options are Incorrect:** * **Option B (High affinity, no intrinsic activity):** This describes a **Competitive Antagonist**. It binds to the receptor but has an intrinsic activity of **0**, producing no response on its own. * **Option C & D (Low affinity):** Affinity determines the potency of a drug, not its classification as an agonist or antagonist. A drug can have low affinity and still be a full agonist if it produces a maximal response once bound. **3. NEET-PG High-Yield Clinical Pearls:** * **Intrinsic Activity Values:** Full Agonist = 1; Partial Agonist = 0 to 1; Antagonist = 0; Inverse Agonist = -1. * **Clinical Examples:** * **Pindolol:** A partial agonist at $\beta$-receptors; used in hypertension to prevent excessive bradycardia. * **Buprenorphine:** A partial $\mu$-opioid agonist used in opioid withdrawal; it has a "ceiling effect" on respiratory depression. * **Varenicline:** A partial agonist at nicotinic receptors used for smoking cessation. * **Aripiprazole:** A partial D2 agonist used in schizophrenia.

Q: Which of the following conditions is most likely due to a pharmacogenetic cause?

Primaquine-induced hemolytic anemia. **Explanation:** **1. Why Option D is Correct:** Primaquine-induced hemolytic anemia is a classic example of a **pharmacogenetic disorder** caused by **Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency**. G6PD is an enzyme essential for maintaining the levels of reduced glutathione in red blood cells (RBCs), which protects them from oxidative stress. Primaquine is an oxidizing drug; in G6PD-deficient individuals, the RBCs cannot neutralize the oxidative stress, leading to hemoglobin denaturation (Heinz bodies) and subsequent hemolysis. This is an X-linked recessive trait, making it a genetically determined abnormal response to a drug. **2. Why Other Options are Incorrect:** * **Option A & B:** Hypoglycemia from insulin and tachycardia from albuterol are **Type A (Augmented)** adverse drug reactions. These are predictable, dose-dependent extensions of the drug’s primary pharmacological action and occur in most individuals if the dose is high enough. * **Option C:** Metoclopramide-induced muscle dystonia is an **Extrapyramidal Side Effect (EPS)** due to central dopamine (D2) receptor blockade. While some individuals are more sensitive, it is generally considered a predictable side effect of the drug's mechanism rather than a specific genetic polymorphism. **3. Clinical Pearls for NEET-PG:** * **Other drugs causing hemolysis in G6PD deficiency:** Sulfonamides, Dapsone, Nitrofurantoin, and Chloroquine. * **Succinylcholine Apnea:** Caused by a genetic deficiency of **Pseudocholinesterase** (Butyrylcholinesterase). * **Slow Acetylators (NAT2 polymorphism):** Increased risk of peripheral neuropathy with **Isoniazid** and SLE-like syndrome with **Hydralazine/Procainamide**. * **Malignant Hyperthermia:** Genetic mutation in **Ryanodine receptors (RyR1)** triggered by Halothane or Succinylcholine.

Q: What does the potency of a drug refer to?

The dose required to produce a specific response. **Potency** refers to the amount or **dose** of a drug required to produce an effect of a given intensity. On a Dose-Response Curve (DRC), potency is represented by the position of the curve along the x-axis (dose) [4]. A drug that produces the same effect at a lower dose is considered "more potent" [2]. **Analysis of Options:** * **Option C (Correct):** Potency is mathematically expressed as the **$EC_{50}$** (the concentration required to produce 50% of the maximum response) [1, 3]. The lower the $EC_{50}$, the higher the potency. * **Option A (Incorrect):** This describes **Affinity**, which is the tendency of a drug to bind to its receptor. While affinity influences potency, they are not synonymous. * **Option B (Incorrect):** This describes **Intrinsic Activity** (Efficacy). It is the ability of a drug to trigger a pharmacological response after binding to the receptor. * **Option D (Incorrect):** This describes **Efficacy** ($E_{max}$). Efficacy is the maximal clinical response a drug can achieve. In clinical practice, efficacy is generally more important than potency. **NEET-PG High-Yield Pearls:** 1. **Potency vs. Efficacy:** On a graph, a shift to the **left** indicates increased potency. A shift **upwards** indicates increased efficacy. 2. **Clinical Relevance:** Potency is rarely a decisive factor in drug choice; it only determines the milligram weight of the tablet [2]. For example, 5mg of Amlodipine is more potent than 50mg of Atenolol, but they are used for different clinical indications [2]. 3. **Relative Potency:** If Drug A produces a response at 10mg and Drug B produces the same response at 100mg, Drug A is 10 times more potent than Drug B [2].

Q: Which of the following drugs acts on -2 receptors?

Clonidine. **Explanation:** The question tests your knowledge of sympathomimetic and sympatholytic drugs and their receptor selectivity. **Correct Answer: C. Clonidine** Clonidine is a prototypical **selective $\alpha_2$-adrenergic agonist**. It acts primarily on presynaptic $\alpha_2$ receptors in the vasomotor center of the medulla. Activation of these receptors inhibits the release of norepinephrine, leading to a decrease in sympathetic outflow to the heart and peripheral vasculature. This results in a reduction in blood pressure, making it a centrally acting antihypertensive. **Analysis of Incorrect Options:** * **A. Phenylephrine:** This is a selective **$\alpha_1$-agonist**. It is commonly used as a nasal decongestant and a vasopressor to increase blood pressure without affecting the heart rate directly (though it may cause reflex bradycardia). * **B. Midodrine:** This is an orally active **$\alpha_1$-agonist** (a prodrug converted to desglymidodrine). It is primarily used in the treatment of symptomatic orthostatic hypotension. * **D. Methoxamine:** This is another selective **$\alpha_1$-agonist** used primarily as a vasopressor to treat hypotension during anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **$\alpha_2$ Agonists:** Apart from Clonidine, other important $\alpha_2$ agonists include **Methyldopa** (drug of choice for hypertension in pregnancy), **Dexmedetomidine** (used for sedation in ICUs), and **Tizanidine** (a central muscle relaxant). * **Clonidine Withdrawal:** Abrupt cessation of clonidine can lead to a "rebound hypertensive crisis" due to a sudden surge in catecholamines. * **Diagnostic Use:** The **Clonidine Suppression Test** is used in the diagnosis of Pheochromocytoma (clonidine fails to suppress catecholamine levels in affected patients).

Q: Atrial Natriuretic Peptide receptors belong to which of the following types of receptors?

Ligand-gated guanylyl cyclase receptor. **Explanation:** **Atrial Natriuretic Peptide (ANP)** and Brain Natriuretic Peptide (BNP) exert their physiological effects by binding to **Natriuretic Peptide Receptor-A (NPR-A)**. This receptor is a classic example of a **transmembrane (membrane-bound) Guanylyl Cyclase**. When ANP binds to the extracellular domain, it directly activates the intracellular catalytic domain of the receptor, which converts GTP into **cyclic GMP (cGMP)**. cGMP then activates Protein Kinase G (PKG), leading to vasodilation and natriuresis. This is distinct from soluble guanylyl cyclase, which is activated by Nitric Oxide. **Analysis of Incorrect Options:** * **A. G-protein coupled receptors (GPCRs):** These utilize secondary messengers like cAMP or $IP_3/DAG$. While many hormones use GPCRs, ANP does not. * **C. Tyrosine kinase receptors:** These (e.g., Insulin, EGF) involve autophosphorylation of tyrosine residues. ANP receptors lack tyrosine kinase activity. * **D. JAK-STAT receptors:** These are used by cytokines and Growth Hormone. They do not have intrinsic enzymatic activity but recruit cytosolic Janus Kinases (JAKs). **High-Yield Clinical Pearls for NEET-PG:** 1. **Dual Role:** ANP receptors are both the receptor and the enzyme (Guanylyl Cyclase). 2. **Sacubitril:** A Neprilysin inhibitor used in Heart Failure (ARNI) that prevents the degradation of ANP/BNP, thereby increasing cGMP levels. 3. **Nesiritide:** A recombinant form of BNP used in acute decompensated heart failure, acting via this same cGMP pathway. 4. **Other cGMP-linked drugs:** Sildenafil (PDE-5 inhibitor) prevents the breakdown of the cGMP generated by these pathways.

Question 1

Therapeutic drug monitoring of plasma concentrations of antihypertensive drugs is not practiced because:

Accepted Answer

It is easier to measure the therapeutic effect of these drugs.

Answer

Determination of plasma level of these drugs is a tedious and long process.

Answer

The antihypertensive effect does not increase linearly with the dose.

Answer

All antihypertensive drugs are prodrugs.

Question 2

Which antitubercular drug metabolism is under genetic control?

Accepted Answer

Isoniazid

Answer

Rifampicin

Answer

Cyclosporine

Answer

Pyrazinamide

Question 3

Pharmacogenetics is associated with:

Accepted Answer

All of these

Answer

Variability of enzyme action

Answer

Individual variability in oral absorption

Answer

Different dose-response relationships in different individuals

Question 4

Therapeutic index of a drug is a measure of its?

Accepted Answer

Safety

Answer

Efficacy

Answer

Potency

Answer

Selectivity

Question 5

A partial agonist has:

Accepted Answer

High affinity but low intrinsic activity

Answer

High affinity but no intrinsic activity

Answer

Low affinity but high intrinsic activity

Answer

Low affinity and low intrinsic activity

Question 6

Which of the following conditions is most likely due to a pharmacogenetic cause?

Accepted Answer

Primaquine-induced hemolytic anemia

Answer

Hypoglycemia caused by insulin

Answer

Tachycardia caused by albuterol

Answer

Metoclopramide-induced muscle dystonia

Question 7

What does the potency of a drug refer to?

Accepted Answer

The dose required to produce a specific response

Answer

Affinity of drug to bind to a receptor

Answer

Affinity of drug that binds to receptors and activates it

Answer

The maximum response a drug can produce

Question 8

Which of the following statements is false?

Accepted Answer

Loading dose is equal to the volume of distribution multiplied by the target plasma concentration.

Answer

Lipid-soluble drugs tend to have a higher volume of distribution.

Answer

The volume of distribution is reduced by high plasma protein binding.

Answer

Half-life is constant in first-order kinetics.

Question 9

Which of the following drugs acts on -2 receptors?

Accepted Answer

Clonidine

Answer

Phenylephrine

Answer

Midodrine

Answer

Methoxamine

Question 10

Atrial Natriuretic Peptide receptors belong to which of the following types of receptors?

Accepted Answer

Ligand-gated guanylyl cyclase receptor

Answer

G-protein coupled receptors

Answer

Tyrosine kinase receptors

Answer

JAK-STAT receptors

Pharmacogenomics — MCQs

Pharmacogenomics — MCQs

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